McDonnell & Miller FS7-4 Switch

The McDonnell & Miller FS7-4 is a heavy-duty, industrial liquid flow switch designed for high-capacity systems requiring precise monitoring of start-stop operations. Engineered with a 1-1/4" NPT connection and a SPDT snap switch, this unit serves as a critical safety interlock for large boilers, chillers, and process cooling applications. It features a maximum operating pressure of 300 PSI and can handle liquid temperatures up to 300°F (149°C). The Part Number 119700 includes trimmable bronze paddles, allowing technicians to calibrate the response based on the specific pipe diameter and flow rate requirements of the job site. The rugged brass housing and stainless steel bellows ensure a leak-proof seal and long-term durability in demanding commercial environments. Whether used for signaling flow in cooling towers or preventing dry firing in hydration systems, the FS7-4 flow switch provides high-sensitivity performance with low pressure drop characteristics typically required by mechanical contractors.

• Universal Compatibility: Trimmable paddles allow for installation in 2" to 16" piping systems.
• High Pressure Rating: Rated for up to 300 PSI, making it suitable for high-stress industrial loops.
• Reliable Switching: Features a Single Pole Double Throw (SPDT) configuration for flexible wiring to alarms or motor starters.
• Robust Construction: Equipped with a brass body and stainless steel components for corrosion resistance.
• Sealed Sensitivity: Bellows-style seal prevents process fluid from contacting the electrical switch assembly.

Can the FS7-4 be used for both increasing and decreasing flow?
Yes, the SPDT snap-action switch allows the unit to be wired to make or break a circuit upon either flow startup or flow failure.

What fluid types are compatible with the trimmable bronze paddles?
This model is designed for water and other non-hazardous liquids. For corrosive chemical applications, a stainless steel model should be considered.

How do I ensure the switch triggers at the correct GPM?
By trimming the provided paddles to the specific pipe size and adjusting the sensitivity screw, you can fine-tune the actuation point for your system's flow requirements.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.